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  • 1.
    Al-Zubaidy, Hussein Mohammed
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Dán, György
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Fodor, Viktoria
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Performance of in-network processing for visual analysis in wireless sensor networks2015In: Proceedings of 2015 14th IFIP Networking Conference, IFIP Networking 2015, IEEE conference proceedings, 2015Conference paper (Refereed)
    Abstract [en]

    Nodes in a sensor network are traditionally used for sensing and data forwarding. However, with the increase of their computational capability, they can be used for in-network data processing, leading to a potential increase of the quality of the networked applications as well as the network lifetime. Visual analysis in sensor networks is a prominent example where the processing power of the network nodes needs to be leveraged to meet the frame rate and the processing delay requirements of common visual analysis applications. The modeling of the end-to-end performance for such networks is, however, challenging, because in-network processing violates the flow conservation law, which is the basis for most queuing analysis. In this work we propose to solve this methodological challenge through appropriately scaling the arrival and the service processes, and we develop probabilistic performance bounds using stochastic network calculus. We use the developed model to determine the main performance bottlenecks of networked visual processing. Our numerical results show that an end-to-end delay of 2-3 frame length is obtained with violation probability in the order of 10-6. Simulation shows that the obtained bounds overestimates the end-to-end delay by no more than 10%.

  • 2. Baroffio, L.
    et al.
    Canclini, A.
    Cesana, M.
    Redondi, A.
    Tagliasacchi, M.
    Dán, György
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Eriksson, Emil
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Fodor, Viktoria
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Ascenso, J.
    Monteiro, P.
    Demo: Enabling image analysis tasks in visual sensor networks2014In: Proceedings of the 8th ACM/IEEE International Conference on Distributed Smart Cameras, ICDSC 2014, Association for Computing Machinery (ACM), 2014, p. a46-Conference paper (Refereed)
    Abstract [en]

    This demo showcases some of the results obtained by the GreenEyes project, whose main objective is to enable visual analysis on resource-constrained multimedia sensor networks. The demo features a multi-hop visual sensor network operated by BeagleBones Linux computers with IEEE 802.15.4 communication capabilities, and capable of recognizing and tracking objects according to two different visual paradigms. In the traditional compress-then-analyze (CTA) paradigm, JPEG compressed images are transmitted through the network from a camera node to a central controller, where the analysis takes place. In the alternative analyze-then-compress (ATC) paradigm, the camera node extracts and compresses local binary visual features from the acquired images (either locally or in a distributed fashion) and transmits them to the central controller, where they are used to perform object recognition/tracking. We show that, in a bandwidth constrained scenario, the latter paradigm allows to reach better results in terms of application frame rates, still ensuring excellent analysis performance.

  • 3. Baroffio, L.
    et al.
    Cesana, M.
    Redondi, A.
    Tagliasacchi, M.
    Ascenso, J.
    Monteiro, P.
    Eriksson, Emil
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Dan, G.
    Fodor, Viktoria
    KTH, School of Electrical Engineering (EES), Communication Networks.
    GreenEyes: Networked energy-aware visual analysis2015In: 2015 IEEE International Conference on Multimedia and Expo Workshops, ICMEW 2015, IEEE conference proceedings, 2015Conference paper (Refereed)
    Abstract [en]

    The GreenEyes project aims at developing a comprehensive set of new methodologies, practical algorithms and protocols, to empower wireless sensor networks with vision capabilities. The key tenet of this research is that most visual analysis tasks can be carried out based on a succinct representation of the image, which entails both global and local features, while it disregards the underlying pixel-level representation. Specifically, GreenEyes will pursue the following goals: i) energy-constrained extraction of visual features; ii) rate-efficiency modelling and coding of visual feature; iii) networking streams of visual features. This will have a significant impact on several scenarios including, e.g., smart cities and environmental monitoring.

  • 4.
    Chatzidrossos, Ilias
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Dán, György
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Fodor, Viktória
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Delay and playout probability trade-off in mesh-based peer-to-peer streaming with delayed buffer map updates2009In: Peer-to-Peer Networking and Applications, ISSN 1936-6442, E-ISSN 1936-6450, Vol. 3, no 3, p. 208-221Article in journal (Refereed)
    Abstract [en]

    In mesh-based peer-to-peer streaming systemsdata is distributed among the peers according tolocal scheduling decisions. The local decisions affecthow packets get distributed in the mesh, the probabilityof duplicates and consequently, the probabilityof timely data delivery. In this paper we proposean analytic framework that allows the evaluation ofscheduling algorithms. We consider four solutions inwhich scheduling is performed at the forwarding peer,based on the knowledge of the playout buffer contentat the neighbors. We evaluate the effectiveness of thesolutions in terms of the probability that a peer can playout a packet versus the playback delay, the sensitivityof the solutions to the accuracy of the knowledge of theneighbors’ playout buffer contents, and the scalabilityof the solutions with respect to the size of the overlay.We also show how the model can be used to evaluatethe effects of node arrivals and departures on the overlay’sperformance.

  • 5.
    Chatzidrossos, Ilias
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Dán, György
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Fodor, Viktória
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Server Guaranteed Cap: an incentive mechanism for maximizing streaming quality in heterogeneous overlays2010In: NETWORKING 2010, PROCEEDINGS / [ed] Crovella M; Feeney LM; Rubenstein D; Raghavan SV, 2010, p. 315-326Conference paper (Refereed)
    Abstract [en]

    We address the problem of maximizing the social welfare in a peer-to-peel streaming overlay given a fixed amount of server upload capacity. We show that peers' selfish behavior leads to an equilibrium that is suboptimal in terms of social welfare, because selfish peers are interested in forming clusters and exchanging data among themselves In order to increase the social welfare we propose a novel incentive mechanism: Server Guaranteed Cap (SGC), that uses the server capacity as an incentive for high contributing peers to upload to low contributing ones We prove that SGC is individually rational anti incentive compatible We also show that under very general conditions, there exists exactly one server capacity allocation that maximizes the social welfare under SGC, hence simple gradient based method can be used to find the optimal allocation

  • 6.
    Chatzidrossos, Ilias
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Fodor, Viktória
    KTH, School of Electrical Engineering (EES), Communication Networks.
    On the effect of free-riders in P2P streaming systems2008In: 2008 4TH INTERNATIONAL TELECOMMUNICATION NETWORKING WORKSHOP ON QOS IN MULTISERVICE IP NETWORKS, 2008, p. 8-13Conference paper (Refereed)
    Abstract [en]

    Peer-to-peer applications exploit the users willingness to contribute with their upload transmission capacity, achieving this way a scalable system where the available transmission capacity increases with the number of participating users. Since not all the users can offer upload capacity with high bitrate and reliability, it is of interest to see how these non-contributing users can be supported by a peer-to-peer application. In this paper we investigate how free-riders, that is, non-contributing users can be served in a peer-to-peer streaming system. We consider different policies of dealing with free-riders and discuss how performance parameters such as blocking and disconnection of free-riders are influenced by these policies, the overlay structure and system parameters as overlay size and source upload capacity. The results show that while the multiple-tree structure may affect the performance free-riders receive, the utilization of the transmission resources is still comparable to that of an optimized overlay.

  • 7.
    Dán, György
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Chatzidrossos, Illias
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Fodor, Viktoria
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks.
    On the performance of error-resilient end-point-based multicast streaming2006In: 2006 14TH IEEE INTERNATIONAL WORKSHOP ON QUALITY OF SERVICE, PROCEEDINGS, 2006, p. 160-168Conference paper (Refereed)
    Abstract [en]

    In this paper we propose an analytical model of a resilient end-node multicast streaming architecture based on multiple minimum-depth-trees that employs path diversity and forward error correction for improved resilience to node churns and packet losses. We study the performance of the architecture in the presence of packet losses and dynamic node behavior. We show that for a given redundancy the probability that an arbitrary node possesses a packet is high as long as the loss probability in the network is below a certain threshold. After reaching the threshold the packet possession probability suddenly drops; the rate decrease gets faster as the number of nodes in the overlay grows. The value of the threshold depends on the ratio of redundancy and on the number of the distribution trees. We study the overlay structure in the presence of node dynamics and conclude that stability can be achieved only if the root node serves a large number of nodes simultaneously.

  • 8.
    Dán, György
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Fodor, Viktoria
    KTH, School of Electrical Engineering (EES), Communication Networks.
    An analytical study of Low Delay Multi-tree-based Overlay Multicast2007In: P2P-TV '07 Proceedings of the 2007 workshop on Peer-to-peer streaming and IP-TV, 2007, p. 352-357Conference paper (Refereed)
    Abstract [en]

    In this paper we propose an analytical model that describes the temporal evolution of the end-to-end loss characteristics for live multicast streaming. We consider push-based architectures combined with retransmissions and forward error correction (FEC). We use the model to identify the primary sources of delay in overlay multicast, and to investigate the possible ways of decreasing the required playback delay. Based on the results we argue that in order to achieve good quality with low playback delays independent of the overlay's size, these systems have to adjust the FEC code rate dynamically. Our findings show that the available upload capacity is the key to efficient overlay multicast with low delay bounds.

  • 9.
    Dán, György
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Fodor, Viktoria
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Delay bounds and scalability for overlay multicast2008In: AD HOC AND SENSOR NETWORKS, WIRELESS NETWORKS, NEXT GENERATION INTERNET, PROCEEDINGS, 2008, Vol. 4982, p. 227-239Conference paper (Refereed)
    Abstract [en]

    A large number of peer-to-peer streaming systems has been proposed and deployed in recent years. Yet, there is no clear understanding of how these systems scale and how multi-path and multihop transmission, properties of all recent systems, affect the quality experienced by the peers. In this paper we present an analytical study that considers the relationship between delay and loss for general overlays: we study the trade-off between the playback delay and the probability of missing a packet and we derive bounds on the scalability of the systems. We use an exact model of push-based overlays to show that the bounds hold under diverse conditions: in the presence of errors, under node churn, and when using forward error correction and various retransmission schemes.

  • 10.
    Dán, György
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Fodor, Viktoria
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    On the efficiency of shaping live video streams2002In: Proceedings of the 2002  international symposium on performance evaluation of computer and telecommunications systems, 2002Conference paper (Refereed)
    Abstract [en]

    In this work the efficiency of shaping live video streams is considered. We propose low complexity shaping algorithms adequate for real-time operation and supporting applications with a wide range of delay tolerance. The effect of shaping is investigated considering video streams multiplexed at an output link with a small buffer to absorb packet scale congestion. The advantage of using small buffers when transmitting video streams is the limited delay and delay variation. Consequently, we concentrate on the loss characteristics to evaluate the performance of the proposed solutions. We present mathematical analysis based on fluid flow modeling and the theory of large deviations and confirm the results with simulation.

  • 11.
    Dán, György
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Fodor, Viktoria
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Quality differentiation with source shaping and forward error correction2003In: Interactive Multimedia On Next Generation Networks / [ed] Ventre, G; Canonico, R, 2003, p. 222-233Conference paper (Refereed)
    Abstract [en]

    The transmission of video traffic over the Internet is a fundamental issue of network design. Video applications require quality of service guarantees from the network in terms of limited packet loss, end-to-end delay, and delay variation. The question of today's research and development is how to provide these guarantees considering the architecture of the present Internet. In the last years a variety of admission control schemes based on per-hop or end-to-end measurements has been suggested to control delay and loss sensitive streams with very little or no support at the routers. Most of these solutions, however, have to apply the same acceptance threshold for all streams, a significant limitation considering the diverse quality requirements of the applications. In this work we investigate how source shaping and forward error correction (FEC) can be used together to achieve application specific quality differentiation in terms of end-to-end delay and packet loss probability. While source shaping and FEC have been proposed independently to decrease the probability of packet loss due to buffer overflow, their joint use has not been studied before. As the two control functions use the same scarce resource, end-node delay, and their efficiency to decrease loss probability is proportional to the introduced delay but with a decreasing marginal gain, combining the two a better performance can be achieved than by using only one of them. The performance evaluation focuses on the optimal delay allocation for shaping and FEC, such that the loss probability is minimized. We investigate how shaping can be used to substitute FEC redundancy and the sensitivity of the quality differentiation to the background traffic characteristics.

  • 12.
    Dán, György
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Fodor, Viktoria
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks.
    A rate-distortion based comparison of media-dependent FEC and MDC for real-time audio2006In: 2006 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS, VOLS 1-12, 2006, Vol. 3, p. 1002-1007Conference paper (Refereed)
    Abstract [en]

    Applications that require low loss probabilities in today's Internet have to employ some end-to-end error-recovery mechanism. For interactive applications with strict delay constraints, the delay introduced by the applied schemes has to be low as well. In this paper we compare two schemes proposed for error recovery for real-time audio applications: media-dependent forward error correction (MD-FEC) and multiple description coding (MDC). We conclude that MDC always performs better than MD-FEC, and that the stationary loss probability plays a key role in the choice of the optimal parameters for these schemes. Combining the analytical results with the loss characteristics of measured traces of VoIP calls we conclude that in the current Internet these schemes give considerable gains for streams with a high code rate only, and for these streams MDC can decrease the average distortion significantly better than MD-FEC.

  • 13.
    Dán, György
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Fodor, Viktoria
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Karlsson, Gunnar
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Analysis of the Packet Loss Process for Multimedia Traffic2004In: Intl. Conference on Telecommunication Systems Modeling and Analysis, 2004Conference paper (Refereed)
    Abstract [en]

    In the case of multimedia traffic, like VBR video, the average loss probability is not sufficient to investigate the effects of loss on perceived visual quality, but it is difficult to analytically model the queuing behavior for such traffic. It has been shown that in the case of realtime communications, for which small buffers are used for delay reasons, short range dependence dominates the loss process and so the Markovmodulated Poisson process (MMPP) might be a reasonable source model. In this paper we present an exact mathematical model for the loss process of an MMPP+M/D/1/K queue; we validate it via simulations and compare it to other mathematical models, like the MMPP+M/M/1/K and the Gilbert model, and to simulations with real MPEG-4 video traces. We conclude that the other models give accurate results only in a small set of network scenarios, while our model can capture the loss process of VBR video sufficiently well in most cases. This makes it possible to analyze the effects of forward error correction on transmission quality in various network scenarios.

  • 14.
    Dán, György
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Fodor, Viktoria
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Are multiple descriptions better than one?2005In: NETWORKING 2005: NETWORKING TECHNOLOGIES, SERVICES, AND PROTOCOLS; PERFORMANCE OF COMPUTER AND COMMUNICATION NETWORKS; MOBILE AND WIRELESS COMMUNICATIONS SYSTEMS / [ed] Boutaba, R; Almeroth, K; Puigjaner, R; Shen, S; Black, JP, 2005, p. 684-696Conference paper (Refereed)
    Abstract [en]

    In this paper we compare three schemes proposed for error recovery for real-time multimedia applications: media-dependent forward error correction (MD-FEC) proposed for real-time audio, media-independent forward error correction (MI-FEC) proposed for real-time video and the recently re-discovered multiple description coding (MDC). We provide a detailed queueing analysis for these schemes considering bursty traffic sources, and combine results from information theory and queueing theory to analyze their performance bounds. We conclude that MDC always performs better than MD-FEC, and that the average loss probability plays a key role in the choice of the optimal parameters. We also show that MDC outperforms MI-FEC if packet losses are highly correlated, like in the current Internet and the available delay for error control is low.

  • 15.
    Dán, György
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Fodor, Viktoria
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks.
    On the asymptotic behavior of end-point-based multicast streaming2006In: 2006 International Zurich Seminar on Communications: Access - Transmission - Networking, Proceedings, NEW YORK: IEEE , 2006, p. 66-69Conference paper (Refereed)
    Abstract [en]

    In this paper we propose an analytical model of a resilient, tree-based end-node multicast streaming architecture that employs path diversity and forward error correction for improved resilience to node churns and packet losses. We show that this architecture can distribute data to nodes arbitrarily far away from the root of the trees as long as the loss probability is lower than a certain threshold, but the probability of packet reception suddenly drops to zero once this threshold is exceeded. The value of the threshold depends on the ratio of redundancy and on the number of the distribution trees.

  • 16.
    Dán, György
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Fodor, Viktoria
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks.
    On the stability of end-point-based multimedia streaming2006In: NETWORKING 2006: NETWORKING TECHNOLOGIES, SERVICES, AND PROTOCOLS; PERFORMANCE OF COMPUTER AND COMMUNICATION NETWORKS; MOBILE AND WIRELESS COMMUNICATIONS SYSTEMS / [ed] Boavida F, Plagemann T, Stiller B; Westphal C, Monteiro E, Berlin: Springer-Verlag Berlin , 2006, p. 678-690Conference paper (Refereed)
    Abstract [en]

    In this paper we propose an analytical model of a resilient, tree-based end-node multicast streaming architecture that employs path diversity and forward error correction for improved resilience to node churns and packet losses. Using the model and via simulations we study the performance of this architecture in the presence of packet losses and dynamic node behavior. We show that the overlay can distribute data to nodes arbitrarily far away from the root of the trees as long as the loss probability is lower than a certain threshold, but the probability of packet reception suddenly drops to zero once this threshold is exceeded. The value of the threshold depends on the ratio of redundancy and on the number of the distribution trees. Using the model and simulations we show that correlated and inhomogeneous losses slightly worsen the overlay's performance. We apply the model to study the effects of dynamic node behavior and compare its results to simulations.

  • 17.
    Dán, György
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Fodor, Viktoria
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Packet size distribution: An aside?2005In: QUALITY OF SERVICE IN MULTISERVICE IP NETWORKS, PROCEEDINGS, 2005, Vol. 3375, p. 75-87Conference paper (Refereed)
    Abstract [en]

    For multimedia traffic like VBR video, knowledge of the average loss probability is not sufficient to determine the impact of loss on the perceived visual quality and on the possible ways of improving it, for example by forward error correction (FEC) and error concealment. In this paper we investigate how the packet size distribution affects the packet loss process, the distribution of the number of packets lost in a block of packets and the related FEC performance. We present an exact mathematical model for the loss process of an MMPP + M/E-r/1/K queue and compare the results of the model to simulations performed with various other packet size distributions (PSDs), among others, the measured PSD from an Internet backbone. We conclude that the packet size distribution affects the packet loss process and thus the efficiency of FEC. This conclusion is mainly valid in access networks where a single multimedia stream might affect the multiplexing behavior. The results show that analytical models of the PSD matching the first three moments (mean,variance and skewness) of the empirical PSD can be used to evaluate the performance of FEC in real networks. We also conclude that the exponential PSD, though it is not a worst case scenario, is a good approximation for the PSD of today's Internet to evaluate FEC performance.

  • 18.
    Dán, György
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Fodor, Viktória
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Delay Asymptotics and Scalability for Peer-to-Peer Live Streaming2009In: IEEE Transactions on Parallel and Distributed Systems, ISSN 1045-9219, E-ISSN 1558-2183, Vol. 20, no 10, p. 1499-1511Article in journal (Refereed)
    Abstract [en]

    A large number of peer-to-peer streaming systems have been proposed and deployed in recent years. Yet, there is no clear understanding of how these systems scale and how multipath and multihop transmission, properties of all recent systems, affect the quality experienced by the peers. In this paper, we present an analytical study that considers the relationship between delay and loss for general overlays: we study the trade-off between the playback delay and the probability of missing a packet and we derive bounds on the scalability of the systems. We present an exact model of push-based overlays and show that the bounds hold under diverse conditions: in the presence of errors, under node churn, and when using forward error correction and various retransmission schemes.

  • 19.
    Dán, György
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Communication Networks.
    Fodor, Viktória
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Communication Networks.
    Stability and performance of overlay multicast systems employing forward error correction2010In: Performance evaluation (Print), ISSN 0166-5316, E-ISSN 1872-745X, Vol. 67, no 2, p. 80-101Article in journal (Refereed)
    Abstract [en]

    The two main sources of impairment in overlay multicast systems are packet losses and node churn. Yet, little is known about their effects on the data distribution performance. In this paper we develop an analytical model of a large class of peer-to-peer streaming architectures based on decomposition and non-linear recurrence relations. We analyze the stability properties of these systems using fixed-point analysis. We derive bounds on the probability that nodes in the overlay receive an arbitrary packet of the stream. Based on the model, we explain the effects of the overlay's size, node heterogeneity, loss correlations and node churn on the overlay's performance. Our findings lead us to the definition of an overlay structure with improved stability properties. We show how and under what conditions overlays can benefit from the use of error control solutions, prioritization and taxation schemes. Based on our results, we identify the components that are needed to achieve good data distribution performance in multi-tree-based overlay multicast.

  • 20.
    Dán, György
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Fodor, Viktória
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Chatzidrossos, Ilias
    KTH, School of Electrical Engineering (EES), Communication Networks.
    On the performance of multiple-tree-based peer-to-peer live streaming2007In: INFOCOM 2007, VOLS 1-5, 2007, p. 2556-2560Conference paper (Refereed)
    Abstract [en]

    In this paper we propose and analyze a generalized multiple-tree-based overlay architecture for peer-to-peer live streaming that employs multipath transmission and forward error correction. We give mathematical models to describe the stability properties of the overlay and evaluate the error recovery in the presence of node dynamics and packet losses. We show how the stability of the overlay improves with the proper allocation of the outgoing bandwidths of the peers among the trees without compromising its error correcting capability.

  • 21.
    Dán, György
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Fodor, Viktória
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Chatzidrossos, Ilias
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Streaming performance in multiple-tree-based overlays2007In: NETWORKING 2007: Ad Hoc and Sensor Networks, Wireless Networks, Next Generation Internet, Proceedings / [ed] Akyildiz, IF; Sivakumar, R; Ekici, E; DeOliveira, JC; McNair, J, 2007, p. 617-627Conference paper (Refereed)
    Abstract [en]

    In this paper we evaluate the data transmission performance of a generalized multiple-tree-based overlay architecture for peer-to-peer live streaming that employs multipath transmission and forward error correction. We give mathematical models to describe the error recovery in the presence of packet losses. We evaluate the data distribution performance of the overlay, its asymptotic behavior, the stability regions for the data transmission, and analyze the system behavior around the stability threshold. We argue that the composed measure of the mean and the variance of the packet possession probability can support adaptive forward error correction.

  • 22.
    Dán, György
    et al.
    KTH, School of Electrical Engineering (EES).
    Fodor, Viktória
    KTH, School of Electrical Engineering (EES).
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES).
    On the effects of the packet size distribution on FEC performance2006In: Computer Networks, ISSN 1389-1286, E-ISSN 1872-7069, Vol. 50, no 8, p. 1104-1129Article in journal (Refereed)
    Abstract [en]

    For multimedia traffic like VBR video, knowledge of the average loss probability is not sufficient to determine the impact of loss on the perceived visual quality and on the possible ways of improving it, for example by forward error correction (FEC) and error concealment. In this paper we investigate how the packet size distribution affects the packet loss process, i.e., the probability of consecutive losses and the distribution of the number of packets lost in a block of packets and the related FEC performance. We present an exact mathematical model for the loss process of an MMPP + MMPP/Er/1/K queue and compare the results of the model to simulations performed with various other packet size distributions (PSDs), among others, the measured PSD from an Internet backbone. The results show that analytical models of the PSD matching the first three moments (mean, variance and skewness) of the empirical PSD can be used to evaluate the performance of FEC in real networks. We conclude that the exponential PSD, though it is not a worst case scenario, is a good approximation for the PSD of today's Internet to evaluate FEC performance. We also conclude that the packet size distribution affects the packet loss process and thus the efficiency of FEC mainly in access networks where a single multimedia stream might affect the multiplexing behavior. We evaluate how the PSD affects the accuracy of the widely used Gilbert model to calculate FEC performance and conclude that the Gilbert model can capture loss correlations better if the CoV of the PSD is high.

  • 23.
    Dán, György
    et al.
    KTH, School of Electrical Engineering (EES).
    Fodor, Viktória
    KTH, School of Electrical Engineering (EES).
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES).
    On the effects of the packet size distribution on the packet loss process2006In: Telecommunications Systems, ISSN 1018-4864, E-ISSN 1572-9451, Vol. 32, no 1, p. 31-53Article in journal (Refereed)
    Abstract [en]

    Real-time multimedia applications have to use forward error correction (FEC) anderror concealment techniques to cope with losses in today's best-effort Internet. The efficiency of these solutions is known however to depend on the correlation between losses in the media stream. In this paper we investigate how the packet size distribution affects the packet loss process, that is, the distribution of the number of lost packets in a block, the related FEC performance and the average loss run length. We present mathematical models for the loss process of the MMPP+M/D/1/K and the MMPP+M/M/1/K queues; we validate the models via simulations, and compare the results to simulation results with an MPEG-4 coded video trace. We conclude that the deterministic packet size distribution (PSD) not only results in lower stationary loss probability than the exponential one, but also gives a less correlated loss process, both at a particular average link load and at a particular stationary loss probability as seen by the media stream.Our results show that for applications that can only measure the packet loss probability, the effects of the PSD on FEC performance are higher in access networks, where a single multimedia stream might affect the multiplexing behavior. Our results show that the effects of the PSD on FEC performance are higher in access networks, where a single multimedia stream might affect the multiplexing behavior and thus can improve the queuing performance by decreasing the variance of its PSD.

  • 24.
    Dán, György
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Fodor, Viktória
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Karlsson, Gunnar
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Robust source-channel coding for real-time multimedia2008In: Multimedia Systems, ISSN 0942-4962, E-ISSN 1432-1882, Vol. 13, no 5-6, p. 363-377Article in journal (Refereed)
    Abstract [en]

    Multimedia applications operating in today's Internet have to employ some form of error resilience to cope with losses. For interactive applications with strict delay constraints the latency introduced by these schemes has to be low as well. Furthermore the parameters of the applied scheme have to be set based on measurements in a possibly rapidly changing environment. In this paper we propose a robust method, called min-max-α, for optimal source-channel code rate allocation to deal with time-varying packet channels and channel state estimation errors. We evaluate its performance when used with forward error correction and multiple description coding in both stationary and non-stationary environments. We show that on a stationary channel robust rate allocation is suboptimal in terms of mean distortion, but it achieves a lower variance, while on a non-stationary channel it prevents severe degradation of the quality. We apply the proposed rate allocation method to motion compensated video and show that it performs better on a non-stationary channel than minimization of the mean distortion proposed earlier.

  • 25.
    Dán, György
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Khan, Muhammadaltamash A.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Fodor, Viktoria
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Characterization of SURF and BRISK interest point distribution for distributed feature extraction in visual sensor networks2015In: IEEE transactions on multimedia, ISSN 1520-9210, E-ISSN 1941-0077, Vol. 17, no 5, p. 591-602, article id 7047857Article in journal (Refereed)
    Abstract [en]

    We study the statistical characteristics of SURF and BRISK interest points and descriptors, with the aim of supporting the design of distributed processing across sensor nodes in a resource -constrained visual sensor network (VSN). Our results show high variability in the density, the spatial distribution , and the octave layer distribution of the interest points. The high variability implies that balancing the processing load among the sensor nodes is a very challenging task, and obtaining a priori information is essential, e.g., through prediction. Our results show that if a priori information is available about the images, then Top-$M$ interest point selection, limited , octave-based processing at the camera node, together with area-based interest point detection and extraction at the processing nodes, can balance the processing load and limit the transmission cost in the network. Complete interest point detection at the camera node with optimized descriptor extraction delegation to the processing nodes in turn can further decrease the transmission load and allow a better balance of the processing load among the network nodes.

  • 26.
    Elek, Viktoria
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Fumagalli, A.
    Wedzinga, G.
    Photonic slot routing: A cost-effective approach to designing all-optical access and metro networks2001In: IEEE Communications Magazine, ISSN 0163-6804, E-ISSN 1558-1896, Vol. 39, no 11, p. 164-172Article in journal (Refereed)
    Abstract [en]

    In the backbone network, the high level of traffic aggregation achieved by numerous users is efficiently served by means of optical circuit switched solutions - the so-called wavelength routing approach. In the access and metro networks, on the contrary, the reduced level of traffic aggregation makes wavelength routing solutions inadequate. The finer and more dynamic bandwidth allocation provided by packet-interleaved optical time-division multiplexing is thus advocated in these network areas. This article presents a survey of an OTDM approach, known as photonic slot routing, or PSR for short. It will be illustrated how this approach may provide a cost-effective solution to deploying all-optical access and metro networks with today's technology.

  • 27.
    Eriksson, Emil
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Dán, György
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Fodor, Viktoria
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Algorithms for Distributed Feature Extraction in Multi-camera Visual Sensor Networks2015In: Proceedings of 2015 14th IFIP Networking Conference, IFIP Networking 2015, IEEE Press, 2015Conference paper (Refereed)
    Abstract [en]

    Real-time visual analysis tasks, like tracking and recognition, require swift execution of computationally intensive algorithms. Enabling visual sensor networks to perform such tasks can be achieved by augmenting the sensor network with processing nodes and distributing the computational burden among several nodes, in a way that the cameras contend for the processing nodes while trying to minimize their completion times. In this paper, we formulate the problem of minimizing the completion time of all camera sensors as an optimization problem. We propose algorithms for fully distributed optimization, analyze the existence of equilibrium allocations, and evaluate their performance. Simulation results show that distributed optimization can provide good performance despite limited information availability at low computational complexity, but the predictable and stable performance is often not provided by the algorithm that provides lowest average completion time.

  • 28.
    Eriksson, Emil
    et al.
    KTH, School of Electrical Engineering (EES), Network and Systems engineering.
    Dán, György
    KTH, School of Electrical Engineering (EES), Network and Systems engineering.
    Fodor, Viktoria
    KTH, School of Electrical Engineering (EES), Network and Systems engineering.
    Distributed Algorithms for Feature Extraction Off-loading in Multi-Camera Visual Sensor Networks2017Report (Other academic)
    Abstract [en]

    Real-time visual analysis tasks, like tracking and recognition, require swift execution of computationally intensive algorithms. Visual sensor networks can be enabled to perform such tasks by augmenting the sensor network with processing nodes and distributing the computational burden in a way that the cameras contend for the processing nodes while trying to minimize their task completion times. In this paper, we formulate the problem of minimizing the completion time of all camera sensors as an optimization problem. We propose algorithms for fully distributed optimization, analyze the existence of equilibrium allocations, evaluate the effect of the network topology and of the video characteristics, and the benefits of central coordination. Our results demonstrate that with sufficient information available, distributed optimization can provide low completion times, moreover predictable and stable performance can be achieved with additional, sparse central coordination.

  • 29.
    Eriksson, Emil
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Dán, György
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Fodor, Viktoria
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Prediction-based Load Control and Balancing for Feature Extraction in Visual Sensor Networks2014Conference paper (Refereed)
    Abstract [en]

    We consider controlling and balancing the processing load in a visual sensor network (VSN) used for detecting local features, such as BRISK. We formulate a prediction problem with random missing data, and propose two regression-based algorithms for data reconstruction. Numerical results illustrate the performance of the proposed algorithms, and show that backward regression combined with the last value predictor can be used for controlling and balancing the processing load in VSNs with good performance.

  • 30.
    Eriksson, Emil
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Dán, György
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Fodor, Viktoria
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Predictive Distributed Visual Analysis for Video in Wireless Sensor Networks2016In: IEEE Transactions on Mobile Computing, ISSN 1536-1233, E-ISSN 1558-0660, Vol. 15, no 7, p. 1743-1756Article in journal (Refereed)
    Abstract [en]

    We consider the problem of performing distributed visual analysis for a video sequence in a visual sensor network that contains sensor nodes dedicated to processing. Visual analysis requires the detection and extraction of visual features from the images, and thus the time to complete the analysis depends on the number and on the spatial distribution of the features, both of which are unknown before performing the detection. In this paper, we formulate the minimization of the time needed to complete the distributed visual analysis for a video sequence subject to a mean average precision requirement as a stochastic optimization problem. We propose a solution based on two composite predictors that reconstruct randomly missing data, on quantile-based linear approximation of feature distribution and on time series analysis methods. The composite predictors allow us to compute an approximate optimal solution through linear programming. We use two surveillance video traces to evaluate the proposed algorithms, and show that prediction is essential for minimizing the completion time, even if the wireless channel conditions vary and introduce significant randomness. The results show that the last value predictor together with regular quantile-based distribution approximation provide a low complexity solution with very good performance.

  • 31.
    Eriksson, Emil
    et al.
    KTH, School of Electrical Engineering (EES), Network and Systems engineering.
    Dán, György
    KTH, School of Electrical Engineering (EES), Network and Systems engineering.
    Fodor, Viktoria
    KTH, School of Electrical Engineering (EES), Network and Systems engineering.
    Radio and Computational Resource Management for Fog Computing Enabled Wireless Camera Networks2016In: Proc. of IEEE GlobeCom Workshop on Internet of Everything, IEEE conference proceedings, 2016Conference paper (Refereed)
    Abstract [en]

    We consider the problem of assigning communication and computing resources of a fog computing system to visual sensors that may observe various scenes from multiple viewing angles. We formulate the Multi-View Assignment Problem (MVAP) as a quadratic mixed-integer problem, and show that it is NP-hard. We propose a polynomial time 4-approximation based on a transformation of MVAP to a General Assignment Problem with dependent profits in which items are sets of sensors with an overlapping field of view, and based on a reduction of the set of items to be assigned. We show that the reduction of the set of items does not affect the solution of the problem if it results in the dominating set of items. Extensive numerical results show that the proposed algorithm performs close to optimal for small systems, performs well even if the reduction finds an approximately dominating set, and scales well with the number of sensors in the system.

  • 32.
    Eriksson, Emil
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Dán, György
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Fodor, Viktoria
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Real-time Distributed Visual Feature Extraction from Video in Sensor Networks2014In: Proceedings - IEEE International Conference on Distributed Computing in Sensor Systems, DCOSS 2014, 2014Conference paper (Refereed)
    Abstract [en]

    Enabling visual sensor networks to perform visual analysis tasks in real-time is challenging due to the computational complexity of detecting and extracting visual features. A promising approach to address this challenge is to distribute the detection and the extraction of local features among the sensor nodes, in which case the time to complete the visual analysis of an image is a function of the number of features found and of the distribution of the features in the image. In this paper we formulate the minimization of the time needed to complete the distributed visual analysis for a video sequence subject to a mean average precision requirement as a stochastic optimization problem. We propose a solution based on two composite predictors that reconstruct randomly missing data, and use a quantile-based linear approximation of the feature distribution and time series analysis methods. The composite predictors allow us to compute an approximate optimal solution through linear programming. We use two surveillance videos to evaluate the proposed algorithms, and show that prediction is essential for controlling the completion time. The results show that the last value predictor together with regular quantile-based distribution approximation provide a low complexity solution with very good performance.

  • 33. Feeney, L. M.
    et al.
    Fodor, Viktória
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Reliability in co-located 802.15.4 personal area networks2016In: MobileHealth 2016 - Proceedings of the 6th MobiHoc International Workshop on Pervasive Wireless Healthcare, Association for Computing Machinery (ACM), 2016, p. 5-10Conference paper (Refereed)
    Abstract [en]

    IEEE 802.5.4-based personal area networks (PANs) are expected to play a key role for emerging mobile health applications. In this work, we evaluate network performance and reliability in the case where several PANs are forced to share the same channel. Based on extensive simulations, we show that inter-network interaction may lead to long periods of disruption, even when the average network performance is very good and the channel is only lightly loaded. We demonstrate that this is mostly due to lack of coordination between networks, rather than limitations of duty cycle or memory.

  • 34. Feeney, L. M.
    et al.
    Frey, M.
    Fodor, Viktoria
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Gunes, M.
    Modes of inter-network interaction in beacon-enabled IEEE 802.15.4 networks2015In: Proceedings of the 2015 14th Annual Mediterranean Ad Hoc Networking Workshop, MED-HOC-NET 2015, IEEE conference proceedings, 2015Conference paper (Refereed)
    Abstract [en]

    Future growth in Internet-of-Things applications will lead to an operating environment with many independent networks operating in the same location. Co-existence and internetwork interference in IEEE 802.15.4 networks is particularly interesting because of the popularity of the radio and limited number of good channels, making it likely that there will be nearby networks operating on the same channel. This paper presents an in-depth simulation study of internetwork interaction between beacon-enabled IEEE 802.15.4 networks using contention-based slotted CSMA and contentionfree GTS allocations. We use simple scenarios intended to highlight the underlying modes of interaction between interfering networks. Our results reveal several complex behaviors, including episodes of large, slow oscillations in throughput and long periods of disconnection interspersed with short bursts of high throughput. These results have practical implications for the design and evaluation of protocols and applications for use in future IoT environments.

  • 35.
    Fodor, Viktoria
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Communication Networks.
    Glaropoulos, Ioannis
    KTH, School of Electrical Engineering (EES), Communication Networks.
    On the gains of deterministic placement and coordinated activation in sensor networks2008In: GLOBECOM 2008 - 2008 IEEE GLOBAL TELECOMMUNICATIONS CONFERENCE   , 2008, p. 335-340Conference paper (Refereed)
    Abstract [en]

    In this paper we discuss topology design and dimensioning of sensor networks to achieve full sensing coverage. We consider two ways of deploying the sensors, placing them according to some regular pattern or scattering them randomly, and two ways of activating the sensors, optimally according to some predefined schedule or randomly, when each sensor follows a wake-up schedule independently from the other sensors. We provide analytic expressions for the necessary and sufficient number of sensors that guarantee coverage in these scenarios and determine the cases when deterministic sensor placement or optimal sensor activation can achieve significant gains. We consider sensing with bounded delay and show that the number of sensors to be deployed can be decreased significantly even at low sensing delays.

  • 36.
    Fodor, Viktoria
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Communication Networks.
    Glaropoulos, Ioannis
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Pescosolido, Loreto
    Detecting low-power primary signals via distributed sensing to support opportunistic spectrum access2009In: 2009 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS, VOLS 1-8, 2009, p. 2819-2824Conference paper (Refereed)
    Abstract [en]

    Cognitive radio operation with opportunistic spectrum access has been proposed to utilize spectrum holes left unused by a primary system owning the spectrum license. The key of cognitive radio operation is the ability to detect weak primary signals and to control the transmission of cognitive users in a way that interference between the two systems is minimized. In this paper we evaluate how a sensor network deployed to provide distributed spectrum sensing can assist cognitive operation. Specifically, we consider sensor networks with regular topology, where a high level of cooperation also means that sensors far from the source of the primary signal are involved in the sensing process. Assuming energy detection and hard-decision combining we derive worst case probabilities of missed detection and false alarm, determine the necessary level of cooperation among the sensors and evaluate how the sensor density and the sensing time affect the performance of distributed sensing.

  • 37.
    Fodor, Viktória
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Communication Networks.
    Chatzidrossos, Ilias
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Playback delay in mesh-based peer-to-peer systems with random packet forwarding2008In: NGMAST 2008: SECOND INTERNATIONAL CONFERENCE ON NEXT GENERATION MOBILE APPLICATIONS, SERVICES, AND TECHNOLOGIES, PROCEEDINGS / [ed] AlBegain K; Cuevas A, LOS ALAMITOS: IEEE COMPUTER SOC , 2008, p. 550-555Conference paper (Refereed)
    Abstract [en]

    In meshed-based peer-to-peer streaming systems peers forward packets to their neighbors based on local scheduling decisions. The local decisions affect how packets get distributed in the mesh, the probability of duplicates and the distribution of the transmission delays. In this paper we propose an analytic framework that allows the evaluation of various scheduling algorithms. We consider two solutions where scheduling is performed at the forwarding peer, based on the knowledge of the playout buffer content at the neighbors. We evaluate the effectiveness of the solutions in terms of the probability that a peer can play out a packet versus the playback delay, and the scalability of the solutions with respect to the size of the overlay.

  • 38.
    Fodor, Viktória
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Communication Networks.
    Chatzidrossos, Ilias
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Playback delay in mesh-based peer-to-peer systems with random packet forwarding and transmission capacity limitations2008In: International Journal of Internet Protocol Technology, ISSN 1743-8209, Vol. 3, no 4, p. 257-265Article in journal (Refereed)
    Abstract [en]

    In meshed-based peer-to-peer streaming systems peers forward packets to their neighbours based on local scheduling decisions. The local decisions affect how packets get distributed in the mesh and consequently the distribution of the transmission delays. We propose an analytic framework that allows the evaluation of various scheduling algorithms. Two solutions are considered where scheduling is performed at the forwarding peer. We evaluate the effectiveness of the solutions in terms of the probability that a peer can play out a packet vs. the playback delay, and the scalability of the solutions with respect to the size of the overlay. Finally we discuss the effects of limited download bandwidth on the data dissemination.

  • 39.
    Fodor, Viktória
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Dán, György
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Resilience in live peer-to-peer streaming2007In: IEEE Communications Magazine, ISSN 0163-6804, E-ISSN 1558-1896, Vol. 45, no 6, p. 116-123Article in journal (Refereed)
    Abstract [en]

    The success of peer-to-peer overlays for live multicast streaming depends on their ability to maintain low delays and a low ratio of information loss end-to-end. However, data distribution over an overlay consisting of unreliable peers is inherently subject to disturbances. Resilience is thus inevitably a key requirement for peer-to-peer live-streaming architectures. In this article, we present a survey of the media distribution methods, overlay structures, and error-control solutions proposed for peer-to-peer live streaming. We discuss the trade off between resilience and overhead and argue that efficient architectures can be defined only through thorough performance analysis.

  • 40.
    Glaropoulos, Ioannis
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Fodor, Viktoria
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Discrete stochastic optimization based parameter estimation for modeling partially observed WLAN spectrum activity2012In: Infocommunications Journal, ISSN 2061-2079, Vol. 4, no 2, p. 11-17Article in journal (Refereed)
    Abstract [en]

    Modeling and parameter estimation of spectrum usage in the ISM band would allow the competing networking technologies to adjust their medium access control accordingly, leading to the more efficient use of the shared spectrum. Tn this paper we address the problem of WLAN spectrum activity model parameter estimation. We propose a solution based on discrete stochastic optimization, that allows accurate spectrum activity modeling and can be implemented even in wireless sensor nodes with limited computational and energy resources.

  • 41.
    Glaropoulos, Ioannis
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Fodor, Viktoria
    KTH, School of Electrical Engineering (EES), Communication Networks.
    On the Efficiency of Distributed Spectrum Sensing in Ad-hoc Cognitive Radio Networks2009In: 2009 ACM WORKSHOP ON COGNITIVE RADIO NETWORKS-CORONET 09, NEW YORK: ASSOC COMPUTING MACHINERY , 2009, p. 7-12Conference paper (Refereed)
    Abstract [en]

    In this work we evaluate the efficiency of cooperative spectrum sensing to support cognitive radio operation, when sensing is assigned to the cognitive users, randomly located in the area of a primary network. We derive analytic expressions for sensing performance based on the traditional metrics of missed detection and false alarm probabilities, and show the existence of an optimal cooperation range. False alarm and missed detection probabilities, however, do not directly lead to performance degradation in the primary and low utilization in the cognitive system. We propose an interference model taking the cognitive access into account and optimize the sensing parameters in order to maximize the cognitive network capacity while satisfying the primary network interference constraints.

  • 42.
    Glaropoulos, Ioannis
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Fodor, Viktoria
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Spectrum sharing with low power primary networks2014In: 2014 IEEE International Symposium on Dynamic Spectrum Access Networks, DYSPAN 2014, IEEE Computer Society, 2014, p. 315-326Conference paper (Refereed)
    Abstract [en]

    Access to unused spectrum bands of primary networks requires a careful optimization of the secondary cooperative spectrum sensing, if the transmission powers in the two networks are comparable. In this case the reliability of the sensing depends significantly on the spatial distribution of the cooperating nodes. In this paper we study the efficiency of cooperative sensing over multiple bands, sensed and shared by a large number of secondary users. We show that the per user cognitive capacity is maximized, if both the number of bands sensed by the secondary network as a whole, and the subsets of these bands sensed by the individual nodes are optimized. We derive the fundamental limits under different sensing duty allocation schemes. We show that with some coordination the per user cognitive capacity can be kept nearly independent from the network density.

  • 43.
    Glaropoulos, Ioannis
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Fodor, Viktoria
    KTH, School of Electrical Engineering (EES), Communication Networks.
    The stability of multiple objective RPL tree formation2015In: Proceedings of the 2015 14th Annual Mediterranean Ad Hoc Networking Workshop, MED-HOC-NET 2015, IEEE conference proceedings, 2015Conference paper (Refereed)
    Abstract [en]

    We address the problem of RPL tree formation in self-organized, multi-hop, wireless sensor networks, where resource-constrained nodes may independently select their routing paths that maximize their performance. We study the result of the tree formation applying a non-cooperative gametheoretic model, and show that multiple objectives may lead to unstable Nash graphs with unwanted traffic cycling. To ensure stability we propose an extension of the node's strategy space, denoted as selective routing, that efficiently eliminates non-acyclic formations from the set of Nash equilibria, while the resulting routing decisions comply with standard.

  • 44.
    Glaropoulos, Ioannis
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Fodor, Viktoria
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    The Stability of Multiple Objective RPL Tree FormationManuscript (preprint) (Other academic)
  • 45.
    Glaropoulos, Ioannis
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Fodor, Viktoria
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Luna, Alexandre Vizcaino
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Papadopouli, Maria
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. Foundation for Research and Technology-Hellas (FORTH) .
    WLAN Channel Occupancy Modeling and Validation2013Conference paper (Other academic)
  • 46.
    Glaropoulos, Ioannis
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Fodor, Viktoria
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Pescosolido, Loreto
    University of Rome "La Sapienza".
    Petrioli, Chiara
    University of Rome "La Sapienza".
    Cognitive WSN Transmission Control for Energy Efficiency under WLAN Coexistence2011In: 2011 6th International ICST Conference on Cognitive Radio Oriented Wireless Networks and Communications, CROWNCOM 2011, 2011, p. 261-265Conference paper (Refereed)
    Abstract [en]

    In this paper we design a cognitive access scheme for WSNs that coexist with WLANs, considering the problem of blind and hidden WLAN terminals. The cognitive access schemerelies on a-priory known WLAN idle time distribution functions and repeated channel measurements to optimize the size of the transmitted data unit and the transmission distance, such that the normalized transmission energy is minimized. We compare the proposed scheme with simple carrier sensing and random access solutions and show that the energy gain is significant under typical WLAN utilization values.

  • 47.
    Glaropoulos, Ioannis
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Laganá, Marcello
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Fodor, Viktoria
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Petrioli, Chiara
    Energy Efficient COGnitive MAC for Sensor Networks under WLAN Co-existence2015In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 14, no 7, p. 18p. 4075-4089Article in journal (Refereed)
    Abstract [en]

    Energy efficiency has been the driving force behind the design of communication protocols for battery-constrained wireless sensor networks (WSNs). The energy efficiency and the performance of the proposed protocol stacks, however, degrade dramatically in case the low-powered WSNs are subject to interference from high-power wireless systems such as WLANs. In this paper we propose COG-MAC, a novel cognitive medium access control scheme (MAC) for IEEE 802.15.4-compliant WSNs that minimizes the energy cost for multihop communications, by deriving energy-optimal packet lengths and single-hop transmission distances based on the experienced interference from IEEE 802.11 WLANs. We evaluate COG-MAC by deriving a detailed analytic model for its performance and by comparing it with previous access control schemes. Numerical and simulation results show that a significant decrease in packet transmission energy cost, up to 66%, can be achieved in a wide range of scenarios, particularly under severe WLAN interference. COGMAC is, also, lightweight and shows high robustness against WLAN model estimation errors and is, therefore, an effective, implementable solution to reduce the WSN performance impairment when coexisting with WLANs.

  • 48.
    Glaropoulos, Ioannis
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Vizcaino Luna, Alexandre
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Fodor, Viktoria
    KTH, School of Electrical Engineering (EES), Communication Networks. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Papadopouli, Maria
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. University of Crete, Heraklion, Greece.
    Closing the gap between traffic workload and channel occupancy models for 802.11 networks2014In: Ad hoc networks, ISSN 1570-8705, E-ISSN 1570-8713, Vol. 21, p. 60-83Article in journal (Refereed)
    Abstract [en]

    The modeling of wireless network traffic is necessary to evaluate the possible gains of spectrum sharing and to support the design of new cognitive protocols that can use spectrum efficiently in network environments where diverse technologies coexist. In this paper we focus on IEEE 802.11 wireless local area networks and close the gap between two popular levels of modeling, macroscopic traffic workload modeling and microscopic channel occupancy modeling. We consider traffic streams generated by established traffic workload models and characterize the networking scenarios where a simple, semi-Markovian channel occupancy model accurately predicts the wireless channel usage. Our results demonstrate that the proposed channel occupancy model can capture the channel idle time distribution in most of the scenarios, while the Markovian assumption cannot be validated in all cases.

  • 49.
    He, Qing
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
    Dán, György
    KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
    Fodor, Viktória
    KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
    Minimizing age of correlated information for wireless camera networks2018In: INFOCOM 2018 - IEEE Conference on Computer Communications Workshops, Institute of Electrical and Electronics Engineers (IEEE), 2018, p. 547-552Conference paper (Refereed)
    Abstract [en]

    Freshness of information is of critical importance for a variety of applications based on wireless camera networks where multi-view image processing is required. In this study, we propose to jointly optimize the use of communication and computing resources such that information from multiple views is delivered is obtained in a timely fashion. To this end, we extend the concept of age of information to capture packets carrying correlated data. We consider the joint optimization of processing node assignment and camera transmission policy, so as to minimize the maximum peak age of information from all sources. We formulate the multi-view age minimization problem (MVAM) and prove that it is NP-hard. We provide fundamental results including tractable cases and optimality conditions. To solve the MVAM efficiently, we develop a modular optimization algorithm following a decomposition approach. Numerical results show that, by employing our approach, the maximum peak age is significantly reduced in comparison to a traditional centralized solution with minimum-time scheduling.

  • 50.
    He, Qing
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
    Dán, György
    KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
    Fodor, Viktória
    KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
    Minimizing Age of Correlated Information for Wireless Camera Networks2018In: IEEE INFOCOM 2018 - IEEE CONFERENCE ON COMPUTER COMMUNICATIONS WORKSHOPS (INFOCOM WKSHPS), IEEE , 2018, p. 547-552Conference paper (Refereed)
    Abstract [en]

    Freshness of information is of critical importance for a variety of applications based on wireless camera networks where multi-view image processing is required. In this study, we propose to jointly optimize the use of communication and computing resources such that information from multiple views is delivered is obtained in a timely fashion. To this end, we extend the concept of age of information to capture packets carrying correlated data. We consider the joint optimization of processing node assignment and camera transmission policy, so as to minimize the maximum peak age of information from all sources. We formulate the multi-view age minimization problem (MVAM) and prove that it is NP-hard. We provide fundamental results including tractable cases and optimality conditions. To solve the MVAM efficiently, we develop a modular optimization algorithm following a decomposition approach. Numerical results show that, by employing our approach, the maximum peak age is significantly reduced in comparison to a traditional centralized solution with minimum-time scheduling.

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